Dithionous acid is a

sulfur oxoacid Sulfur oxoacids are chemical compounds that contain sulfur, oxygen, and hydrogen. The best known and most important industrially used is sulfuric acid. Sulfur has several oxoacids; however, some of these are known only from their salts (these are s ...

with the chemical formula H₂S₂O₄. It is unstable in pure form, but its

salts In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...

, known as

dithionite The dithionite is the oxyanion with the formula 2O4sup>2−. It is commonly encountered as the salt sodium dithionite. For historical reasons, it is sometimes called hydrosulfite, but it contains no hydrogen and is not a sulfite. The dianio ...

s, are stable. It was initially assumed that the ''C''₂ symmetric structure HOS(=O)-S(=O)OH is the most stable among molecules with the formula using

ab initio calculation ''Ab initio'' quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excite ...

s. The reason for this is the existence of intermolecular hydrogen bonds. It is now known that dithionous acid spontaneously decomposes to SO₂ and S(OH)₂. Sodium dithionite is a white powder used as a

reductant In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

and a

bleaching Bleach is the generic name for any chemical product that is used industrially or domestically to remove color (whitening) from a fabric or fiber or to clean or to remove stains in a process called bleaching. It often refers specifically, to ...

agent. It is also used to reduce the

nitro group In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitr ...

to an

amino group In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

in organic reactions.

References

Sulfur oxoacids Dithionites {{inorganic-compound-stub